Oxidation of higher olefins in the presence of iridium metal

ABSTRACT

AN OLEFIN HAVING FROM THREE TO EIGHT CARBON ATOMS PER MOLECULE, SUCH AS PROPYLENE, IS OXIDIZED WITH OXYGEN TO FATTY ACIDS AND OTHER OXYGENATED COMPOUNDS, SUCH AS ACETIC ACID, ACROLEIN, ETC., BY OXIDATION OF THE OLEFIN IN THE CONTACT PRESENCE OF IRIDIUM METAL.

United States Patent 3,644,511 OXIDATION OF HIGHER OLEFINS IN THE PRESENCE OF IRIDIUM METAL Noel W. Cant and William K. Hall, Pittsburgh, Pa., as-

signors to Gulf Research & Development Company, Pittsburgh, Pa.

No Drawing. Continuation-impart of application Ser. No. 778,805, Nov. 25, 1968. This application Sept. 16, 1969, Ser. No. 858,514

Int. Cl. C07c 45/04, 53/08 US. Cl. 260-533 R 11 Claims ABSTRACT OF THE DISCLOSURE An olefin having from three to eight carbon atoms per molecule, such as propylene, is oxidized with oxygen to fatty acids and other oxygenated compounds, such as acetic acid, acrolein, etc., by oxidation of the olefin in the contact presence of iridium metal.

This application is a continuation-in-part of our copending Ser. No. 778,805, filed Nov. 25, 1968 and assigned to the same assignee as the present application.

This invention relates to a process for oxidizing an olefin having from three to eight carbon atoms per molecule to obtain a useful mixture of organic compounds comprising a primary acid and/or a ketone.

In addition to the above desired compounds, by products such as carbon dioxide and water are formed. It was expected that the partial oxidation of olefins having three to eight carbon atoms would yield primarily organic acids containing the same number of carbon atoms as the starting olefin. Quite unexpectedly, it has been found that the main course of the reaction is to cleave the olefin at its double bond which results in the production of substantial yields of lower carbon number oxidized products comprising primary acids (fatty acids) and ketones containing lesser numbers of carbon atoms than the starting olefins, and much smaller amounts of ketones, diones and unsaturated aldehydes having the same number of carbon atoms as the starting olefin so long as the oxidation reaction is carried out in the contact presence of iridium metal.

In accordance with the invention, therefore, an olefin having from three to eight carbon atoms is oxidized to a product comprising a fatty acid by reacting the olefin with a gas containing free molecular oxygen in the contact presence of iridium metal.

The charge stock can be any aliphatic olefin or mixture of olefins having from three to eight carbon atoms per molecule, preferably from three to six carbon atoms. The olefin can be straight-chain or branched-chain in structure. The olefin can be a terminal (alpha) olefin or an internal olefin. The most preferred olefins are the straight-chain alpha-olefins having from three to five carbon atoms per molecule. Suitable olefins include propylene; cis-Z-butene; trans-Z-butene; l-butene; isobutene; Z-pentene; l-pentene; l-hexene; 2-hexene; l-heptene; 2-heptene; 3,4-dimethylpentene-l; l-octene; and 3-octene.

The olefins may he obtained from any suitable source and their method of preparation is not critical to this invention. Refinery streams, such as a refinery propanepropylene stream, can suitably be employed.

The type of olefin determines the type of oxidation product which is obtained since the main reaction is cleavage of the olefin at the double bond. For example, an aliphatic straight-chain olefin Patented Feb. 22, 1972 ice where the olefinic bond can be terminal or internal will always produce an oxidation product comprising a fatty acid; the vinylidene olefins (R C=CH yield a product comprising a ketone; and the trisubstituted olefins yield a product comprising a ketone and an acid. The vinylidene type olefins have, of course, from four to eight carbon atoms per molecule, while the trisubstituted olefins have from five to eight carbon atoms.

Whenever the term olefin is used in this specification, the term is meant to include any of the olefins specifically set forth above or mixtures of the same.

In order to obtain good selectivity to the desired oxygenated compounds it is important that the olefin together with a gas containing free molecular oxygen be contacted with the iridium metal either supported or unsupported at a temperature within the range of about 50 C. to about 300 C., and preferably within the range of about C. to about 200 C. Since the reaction is exothermic, means must be provided to control the temperature of the reaction within the limits defined above. Below the lower temperature limits defined above the reaction rate becomes too low to be economically feasible, whereas at temperatures above the upper limits the yield of desired oxygenated compounds decreases with the concurrent production of excessive amounts of water and carbon dioxide. The temperature can be controlled by any suitable means, and one method of at least partially controlling the temperature is to dilute the iridium metal by distending it on a suitable support material such as silica, magnesia, alumina, thoria or mixtures thereof. The iridium metal can, of course, be used unsupported and when this is done the metal can be in any suitable form, such as sponge form. When the iridium is distended on a support, the surface area of the support is not critical and can suitably be between 0.1 and 600 square meters per gram. In addition to the above named supports, materials such as carbon, kieselguhr, pumice, the natural clays, mullite and Alundum are also suitable. When the iridium metal is supported, suitable amounts of iridium metal are from 0.2 to 30 weight percent of the total catalyst with preferred amounts from one to ten weight percent and the more preferred amounts from one to five weight percent of the total catalyst.

The method of preparing the supported or unsupported catalysts is not critical. Suitable methods of preparing the supported catalysts, for example, include the method of incipient wetness using aqueous solutions of suitable iridium salts such as H IrCl followed by drying and reduction in hydrogen to obtain the metal.

Another method of controlling the temperature is to dilute the olefin-oxygen mixture with an inert gas such as nitrogen or helium. Yet another method of controlling the reaction temperature is to pass the admixture of olefin and oxygen over the iridium metal catalyst at very high space velocities. Suitable gaseous space velocities are within the range of about one to 2000 volumes of olefin measured -at standard temperature .and pressure per volume of catalyst per hour, and the preferred space velocities are from about five to about 200.

A total operating pressure of about one atmosphere is the desired operating pressure. Higher or lower pressuers can be used; for example, pressures of from 0.5 to 15 atmospheres or more can suitably be employed.

The ratio of the partial pressure of oxygen to the partial pressure of olefin can suitably be between 0.2 and 100, and is preferably between two and 30. The partial pressure of olefin should be at least 0.01 p.s.i.a. and is preferably from 0.05 to one p.s.i.a. when the total pressure is atmospheric (14 p.s.i.a.). correspondingly higher partial pressures of olefin would be employed at correspondingly higher total operating pressures.

The olefin is oxidized in the presence of a gas containing free molecular oxygen. Pure oxygen can be used, but this creates problems of temperature control as noted above. It is preferred that the free molecular oxygen be diluted with an inert gas such as nitrogen or helium. The volume percent of free molecular oxygen in the gas containing it can suitably be between one and 100 and is preferably between one and 20. When an olefin is mixed with this gas containing free molecular oxygen, the partial pressure of oxygen is usually between 0.5 and ten p.s.i.a. and is preferably between two and five p.s.i.a. If the partial pressure of oxygen is below about 2.0 pounds per square inch absolute, selectivity to the desired oxygenated products decreases, whereas about two pounds per square inch absolute selectivity to the desired oxygenated compounds remains substantially constant.

The invention will be further described with reference to the following experimental work. In all of the examples to follow, the following procedure was employed. A single pass flow system was used wherein a feed mixture 4 EXAMPLE 1 In the run for this example, a feed mixture containing propylene as the olefin was passed through a bed of an alpha-alumina supported iridium catalyst containing 1.5 weight percent iridium. The results of this run are summarized in Table I below.

EXAMPLE 2 In the run for this example, the feed mixture utilizing propylene as the olefin was passed through a bed of a silica supported iridium catalyst containing five weight percent iridium. The silica support was a commercial Cab- O-Sil material obtained from the Cabot Company. The catalyst was prepared by the method of incipient wetness by contacting the Cab-O-Sil with an aqueous solution of an appropriate amount of an iridium salt, i.e. H IrCl drying the material and reducing at 300 C. in hydrogen to convert the salt to metallic iridium. The results of this run are summarized in Table I below.

Referring to Table I below, the percent selectivity to the useful oxygenated products was about the same (30.5 v. 28) for the alpha-alumina supported iridium catalyst (Example 1) as with the silica supported iridium catalyst (Example 2) at about the same oxidation rate.

TABLE I [Products of propylene oxidation Over supported iridium at a total pressure of about 740 mm.

Oxida- Total tion 2 Percent selectivity 3 to percent Partial rate selec- Partial pressure vol- Acrylic tivity Weight pressure propyl- Temperumes. plus Acrolem to useful Example percent oxygen ene ature CaHe/ Acetic propiomc plus oxygenated Number Metal Support metal (mm.) (mm.) C.) min. ac acid acetone products 1 Ir a-AlzOa 1. 131 7 135 0. 0. 5 5.0 30. 5 2 I1 S10: 5. 0 61 21 185 0. 18 21 3 4 28 1 The {low rate was about 2,500 volumes of total feed per hour.

2 The oxidation rate is defined as the rate at which propylene is converted to all products in volumes (STP) per minute. e.g. it the propylene is passed over the catalyst at two volumes per minute and it is found that 1.8 volumes per minute is recovered unchanged, then the oxidation rate is 2.0 minus 1.8. or 0.2 volumes per minute.

B The percent selectivity is defined as the percent of the propylene oxidized which is converted to the given product.

TABLE II [D epcndcnce of rate and selectivity propylene oxidation over 1.50: Ir/AIZOa on process variables] Oxy- Pro- Oxidagen pylene tion Percent selectivity 3 to- Temperprespresrate 2 Example ature sure sure v0ls./ Acetic number 0.) (mm). (mm.) min. acid Acetone Acrolein 3 See table I footnotes.

ot' olefin, oxygen and helium was passed at atmospheric pressure through a bed (approximately two parts by volume of catalyst) of a supported iridium catalyst at a given temperature between 50 C. and 200 C. at a flow rate of between 2400 and 6000 volumes of total feed per hour. The contact time was between one and three seconds and the space velocity based on the total feed was between 1500 and 3000 volumes of feed per volume of catalyst per hour. The reaction products were cooled to 80 C. by indirect cooling to condense the reaction product which was mostly acetic acid with minor amounts of acetone, acrolein, acrylic and/ or propionic acids. Water and CO were formed as by-products.

A series of runs was made by passing a feed mixture containing varying amounts of oxygen, propylene and helium over the catalyst of Example 1 at varying conditions to determine the effect of changes in temperatures and feed composition on reaction rate and selectivity to the production of acetic acid, acetone and acrolein. The results of this series of runs are given in Table II above.

Referring to Table II above, it can be seen that the selectivity to the production of acetic acid, acetone and acrolein decreases slightly in going from C. to 123 C. (compare Examples 38). The rate, however, increases considerably with the increase in temperature (again compare Examples 3-8). The rate of oxidation increases with propylene pressure as can be seen by comparing Examples 9-13. The oxidation rate is not greatly alfected by the oxygen partial pressure, but the percent selectivity to useful oxygenated products increases with an increase in oxygen partial pressure as can be seen by a comparison of Examples 14-18.

A series of runs was made by passing a feed mixture differing in the olefin employed over the catalyst of Examples 1 or 2 at approximately the same conditions in order to determine the conversion of the olefin and the selectivity to various oxygenated products. The results of this series of runs are given on Table III below.

It will be seen from Table III that at a given temperature the alpha-olefins (propylene and l-butene) are oxidized much more rapidly than the internal or branched olefins.

The product distribution indicates the main reaction is cleavage of the olefin at the double bond to yield an acid or a ketone in the case of an internal olefin, such as isobutylene, where the production of an acid is not possible. This main reaction accounts for the formation of acetic acid from cisand trans-2-butene; propionic acid from l-butene; acetone from isobutene and both acetic and propionic acids from 2-pentenes. The formation of acetic acid from l-butene and isobutene may result from the isomerization of these olefins (on the catalyst surface) to Z butenes prior to oxidation. This is probably the mechanism, although it is not certain, since transand cis-2- butenes appeared in the unoxidized product of the l-butene oxidation (see Example 22 and footnote 1 of Table III).

TABLE III 6 under oxidation conditions with a gas containing free molecular oxygen in the contact presence of iridium metal.

2. A process for the production of a product comprising a fatty acid, which process comprises reacting an aliphatic straight chain olefin or a trisubstituted olefin of the formula /C==CR R Where R is alkyl, said olefins having from 3 to 8 carbon atoms under oxidation conditions with a gas containing free molecular oxygen in the contact presence of iridium metal.

3. A process for the production of a product comprising a ketone, which process comprises reacting a vinylidene type olefin of the formula /C=C/ R H where R is alkyl or a trisubstituted olefin of the formula o= JR [Oxidation of olefins over supported iridium catalysts] Selectivity to products, percent All Par- Parther tlal tial partlprespresally sure sure oxy- Temperoleoxy- Conver- Progenated Example ature fin gen sion 1 Acetic plonic pronumber Olefin Catalyst 0.) (mm) (mm.) percent acid acid Acetone duets 3 l9 Propylene. 156 4 50 90 25-30 2. 0 3. 0 1 20-... Cis-2-butene. 155 4' 50 34 0. 4 0. 2 6 21 Trans-2-butene 0 155 4 50 20 32 0. 5 0. 2 6 22 1 2 155 4 50 80 20 15. 0 0. 2 4 23 155 4 50 20 8 0. 5 12. 5 4 24 2-pentene 5 153 4 70 35 10. 0 0. 2 4 25 Trans-2-butene-. Ir/oz-AlOz 153 4 15 28 0. 5 0. 2 4

1 The total flow rate in these experiments was 5,400 volumes of total feed per hour in all cases except for 2-pentene when a total flow of 2,700 volumes of total feed per hour was employed.

2 The selectivities are calculated on the basis that one molecule of each product is produced for each mole of olefin oxidized. 1 Other partially oxygenated products formed in detectable amounts were as follows (none amounted to more than 3%): From propylene-aerolein; from n butenes-meth yl ethyl ketone, methyl vinyl ketone, 2,3-butanedione and butadiene; from iso-buteuemethacrolein and saturated and unsaturated Q4 acids; from 2-pentene-saturated and unsaturated C5 ketones.

4 Some isomerization under reaction conditions. At this conversion level, the unreactcd butenes had the composition: 73%

l-butene, 23% trans-2-butene and 4% cis-2-butene.

6 The starting pentene was 72% cis-2-pentene; 28% trans-2-pentene.

The oxidation of other olefins within the defined range yields fatty acids and ketones as the primary products. Thus, n-pentanoic acid is the product of l-hexene oxidation; n-butanoic acid and acetic acid are the products of Z-hexene oxidation; propionic acid is the product of 3- hexene oxidation; and acetone and propionic acid are the products of 2-methyl-2-pentene oxidation. Other olefins within the defined range are expected to cleave at the double bond to produce the acid and/ or ketone as above. Some isomerization also occurs during oxidation, thus producing other acids and ketones.

Obviously, many modifications and variations of the invention as hereinabove can be made without departing from the spirit and the scope thereof, and such modifications and variations are intended to be included within the scope of this invention.

We claim:

1. A process which comprises oxidizing a hydrocarbon olefin having from 3 to 8 carbon atoms per molecule where R is alkyl, said olefins having from 4 to 8 carbon atoms per molecule under oxidation conditions with a gas containing free molecular oxygen in the contact presence of iridium metal.

4. A process according to claim 1 wherein the reaction occurs at a temperature from 50 C. to 300 C., a partial pressure of oxygen above about 0.5 pounds per square inch absolute and an olefin space velocity from about one to about 2000.

5. The process of claim 4 wherein the temperature in the reaction zone is maintained in the range of from about C. to about 200 C.

6. A process according to claim 4 wherein the partial pressure of oxygen is Within the range of about 0.5 to about 10 pounds per square inch absolute.

7. The process of claim 1 wherein the iridium metal is deposited on a support.

8. A process according to claim 7 wherein the reaction References Cited occurs at a temperature from 50 C. to 300 C. and the UNITED STATES PATENTS amount of iridium metal is from 0.2 to 30 weight percent 3,534,093 10/1970 Gerberich et al. 260-533 X the mm catalyst 3,439,044 4/1969 Hirsch et a1. 260-604 A 9. A process accordmg to claim 8 wherein the support 5 is alpha-alumma- LORRAINE A. WEINBERGER, Primary Examiner 10. A process according to claim 8 wherein the sup- R D KELLY Assistant Examiner port is silica.

11. A process according to claim 2 wherein the olefin 10 US, Cl. X R, is Z-butene. 260597 B, 604 AC UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTIGN Patent No. 3,644,511 Dated F bruary 22, 1972 Noel W. Cant and William K. Hall Inventor(s) It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below;

3, line 17, "whereas about two pounds" should read -whereas above about two pounds;

Col. 4, Table II, that part of the title which reads "1. Son Ir/Al O "v should read --l.5% Ir/oLAl O Signed and sealed this 8th day of August 1972.

(SEAL) Attest:

EDWARD I LFLETCHER JR ROBERT GUTTSCHALK Attesting Officer Commissioner of Patents 

